4.1 空间及磁盘路径

--ASM磁盘组使用情况  used_percent, asm实例无法使用计算
col name format a15
set lines 200
with  temp_asm as (select name,trunc(free_mb/1024,2) free_gb,trunc(total_mb/1024,2) total_gb,trunc(REQUIRED_MIRROR_FREE_MB/1024,2) req_free_gb,trunc(USABLE_FILE_MB/1024,2) uf_gb,type,state from v$asm_diskgroup)
select * from (
select t.*,trunc((total_gb-free_gb)/total_gb*100,2) as used_percent from temp_asm t where type='EXTERN' union all
select t.*,trunc(((total_gb-free_gb)/2)/((total_gb-req_free_gb)/2)*100,2) as used_percent from temp_asm t where type='NORMAL' union all
select t.*,trunc(((total_gb-free_gb)/3)/((total_gb-req_free_gb)/3)*100,2) as used_percent from temp_asm t where type='HIGH')
order by used_percent desc;
--or
select name,free_mb,total_mb,type,state from v$asm_diskgroup;
--检查磁盘信息
set pages 999
col path format a20;
col group_name format a15
col name format a20
col FAILGROUP_TYPE format a15
col FAILGROUP format a20
col state for a10
select a.group_number,b.name as group_name,a.FAILGROUP,a.name,a.path,a.state,a.total_mb from v$asm_disk a,v$asm_diskgroup b where a.group_number=b.group_number;

4.2 磁盘修复检查

#验证asm磁盘组
kfod asm_diskstring='/dev/mapper/*' disks=all
kfed read /dev/mapper/data1 |grep grpname
#asm 读取磁盘头
kfed read /dev/raw/raw2 text=/tmp/asmdisk_raw2.txt  
kfed read /dev/raw/raw2 aun=0 blkn=0
kfed read /dev/raw/raw2  blkn=510 > /tmp/1.txt 
kfed read /dev/raw/raw2 aun=1 blkn=254
#修复磁盘头
kfed write /dev/raw/raw2 aunum=0 blknum=0 text=/tmp/asmdisk_raw2.txt
#or
dd if=/dev/raw/raw2 of=/tmp/raw2.txt   skip=510 bs=4096 count=1
dd if=/tmp/raw2.txt of=/dev/raw/raw2

4.3 ASM相关视图

4.4 ASM内部视图X$KFFXP

X$KFFXP是ASM(Automatic Storage Management)自动存储管理特性的重要内部视图，该视图反应了File Extent Map映射关系，ASM会将文件split成多个多个piece分片，这些分片被称为Extents。 在Disk上存放这些Extent的位置，就是我们常说的”Allocation Unit”。

KFF意为Kernel File，X$KFFXP即Kernel File Extent Maps， 该内部视图的一条记录代表一个Extent

字段含义如下：

GROUP_KFFXP        diskgroup number (1 - 63) ASM disk group number. Join with v$asm_disk and v$asm_diskgroup
NUMBER_KFFXP      file number for the extent ASM file number. Join with v$asm_file and v$asm_alias
COMPOUND_KFFXP    (group_kffxp << 24) + file # File identifier. Join with compound_index in v$asm_file
INCARN_KFFXP      file incarnation number File incarnation id. Join with incarnation in v$asm_file
PXN_KFFXP            physical extent number  Extent number per file
XNUM_KFFXP          extent number bit 31 set if indirect Logical extent
number per file (mirrored extents have the same value)
LXN_KFFXP            logical extent number 0,1 used to identify primary/mirror extent,
2 identifies file header allocation unit (hypothesis) used in the query such that
we go after only the primary extents, not secondary extents 
DISK_KFFXP          disk on which AU is located  Disk number where the extent is allocated.
Join with v$asm_disk Relative position of the allocation unit from the beginning of the disk. 
AU_KFFXP              AU number on disk of AU allocation unit size (1 MB) in v$asm_diskgroup
#从11g开始加入了CHK_KFFXP SIZE_KFFXP 2个新的字段
CHK_KFFXP   未知 可能是范围为[0-256]的某种校验值
SIZE_KFFXP  size_kffxp is used such that we account for variable sized extents. 
sum(size_kffxp) provides the number of AUs that are on that disk.

在实例级别控制ASM Diskgroup AU 和 stripe size的是2个隐藏参数 _asm_ausize 1048576 以及 _asm_stripesize 131072。从11g开始一个Extent可能包含多个AU。

可以通过以下脚本查询文件与Extent等ASM属性的映射关系:

set linesize 140 pagesize 1400
col "FILE NAME" format a40
set head on
select NAME         "FILE NAME",
       NUMBER_KFFXP "FILE NUMBER",
       XNUM_KFFXP   "EXTENT NUMBER",
       DISK_KFFXP   "DISK NUMBER",
       AU_KFFXP     "AU NUMBER",
       SIZE_KFFXP   "NUMBER of AUs"
  from x$kffxp, v$asm_alias
 where GROUP_KFFXP = GROUP_NUMBER
   and NUMBER_KFFXP = FILE_NUMBER
   and system_created = 'Y'
   and lxn_kffxp = 0
 order by name;

4.5 条带化原理和rebalance

条带化

ASM的条带化有两种：coarse和fine-gained 。AU是最小空间分配单元，缺省是1M，每个AU缺省由8个128K条带空间组成。

• 在coarse条带化中，一个磁盘对应一个AU
  所以该条带化适合连续的I/O读写，比如全表扫描表
• 在fine-gained条带化里，一个AU中的8个128K条带空间，平均打散在磁盘上
  也就是说，4个磁盘，1个AU是平均分布在4个磁盘，每个磁盘2个128K
  适合于对数据读写延迟比较敏感的文件。如redo日志，控制文件，spfile等

重平衡

从diskgroup中添加或删除disk时候，将触发RBAL进程创建rebalance计划、计算时间开销.而后、发消息给ARBn进程（ASM Reblance）处理该请求
ARBn进程对每个extents进行locked, relocated和unlocked操作，执行过程中可以参考v$asm_operation视图.
ARBn进程的数量由参数ASM_POWER_LIMIT决定,
COD (Continuting Operation Directory)用于记录rebalances情况
如果rebalance失败，在重启instance时候，将从COD读取记录，重新启动rebalance
注意事项：

• rebalance仅仅在diskgroup发生改变时候才进行的，并不是定时执行
  如果rebalance执行过程中，server宕机，重启后会自动进行rebalance

• 每个disk的大小必须是相同，如果存在一个小盘，因为rebalance将对每个盘的分配相同比例的空间，可能造成rebalance时候空间不足
  如果执行过程中，空闲空间不足，造成rebalance失败，将出现ORA-15041错误，需要再添加disk
  如果需要频繁添加disk，每一次都可能造成数据的频繁移动，为提高效率，最好批量添加
  如果磁盘大小一样，仍然没有进行rebalance，需要查看asm_power_limit

参考

• https://www.askmaclean.com/archives/know-oracle-asm-basic-html.html
• https://blog.csdn.net/iteye_4537/article/details/82130124